Amoonguss provides an excellent partner to Trick Room teams with Rage Powder and Spore, but can work well even outside of Trick Room thanks to its huge natural bulk and access to Spore.

Good partners for Amoonguss are powerful Trick Room attackers, since it's unable to do much damage itself. Since Amoonguss struggles against Steel-types, a Ground- or Fighting-type partner such as Hariyama or Rhyperior can be an effective partner. Amoonguss's ability to stop most Fighting-types such as Hitmontop in their tracks with Spore allows it to help Pokemon such as Tyranitar that are weak to Mach Punch.

Amoonguss can opt to run more Speed to screw over slower Amoonguss and the majority of Trick Room teams, but it does detract from Amoonguss's bulk.

Recommend Occa Berry as that is the main thing that KOs it now. That should be the first item slot then followed by Mental Herb and finally Coba Berry. I have an EV spread meant to survive Abomasnow's Blizzard while the rest goes into defense because physical attacks are still used and it is never good to be 3HKOd by Terrakion's Rock Slide.

Amoonguss with the given spread doesn't die to any special Fire attack, even in sun, but Occa's certainly an option. Since Amoonguss eats Terrakion alive anyway, that spread isn't mandatory, but it's certainly useful, and it's been added.